The present invention relates to bearings for a rotating assembly, and more specifically to a thrust bearing for counteracting axial thrust acting on a rotating shaft.
Thrust bearings may be used in a wide variety of rotating machinery such as, but not limited to, pumps, turbines and motors. Thrust bearings limit axial movement of the rotating body that is subject to a force acting in a direction parallel to the axis of rotation. Thrust bearings, however, permit the rotation of the rotating body. Sources of axial thrust include the weight of a rotor or pressure differentials within a rotating machine.
One type of thrust bearing is a roller-type. Roller-type thrust bearings use ball or cylindrical bearings to prevent the axial movement of a shaft. This type of bearing, however, is undesirable since they must be machined to highly accurate dimensions and thus are expensive. Roller-type bearings are also prone to failure if minor lubrication contamination or high operating temperatures are experienced.
Another type of thrust bearing is a sliding contact bearing. The rotating portion of the bearing is called the runner and the stationary portion of the sliding contact bearing is called the bearing. A sliding contact bearing uses a lubricant between the bearing and the runner to reduce sliding friction. A fluid film thrust bearing maintains an unbroken film of lubricant between the bearing and the runner to achieve low frictional drag and a low rate of wear. These positive attributes are achieved since the bearings and runner do not come in contact during operation.
There are two basic types of sliding contact thrust bearings; the hydrostatic type and the hydrodynamic type. In prior art FIG. 13, a port 110 through a bearing 112 is used to provide a fluid pressure between bearing 112 and a rotating shaft 114. The fluid pressure within cavity 116 is used to counteract the axial thrust represented by arrow 118. If the axial thrust and the fluid pressure within cavity 116 are in balance, the rotating shaft 114 will not change axial position. During normal operation of rotating machinery, however, the axial force acting on rotor may vary. Thus, the sliding contact thrust bearing of prior art FIG. 13 does not possess the ability to regulate the fluid pressure within cavity 116.
Referring now to prior art FIG. 14, a runner 120 is mounted on the end of rotating shaft 114. An orifice plate 122 is used to regulate the flow of pressure into port 110. Bearing 112 has sealing faces 124 that are directly opposite the runner 120. If an axial force on rotating shaft 114 forces the rotating shaft closer to bearing 112, the increased pressure within cavity 116 will force runner 120 away from sealing surfaces 124. Conversely, if an axial force forces rotating shaft 114 in a direction away from bearing 112, pressure from within cavity 116 will be released between runner 120 and sealing surfaces 124. Orifice plate 122 regulates the flow of fluid into cavity 116. If runner 120 moves a distance away from bearing 112 because of low axial force, then the lubricant flow rate would increase if no orifice plate 112 is present. By limiting the flow of fluid into cavity 116, the pressure in fluid reservoir reduces and causes runner 120 to move toward bearing 112.
A hydrostatic type sliding contact thrust bearing such as that illustrated in prior art FIGS. 13 and 14 are not suitable for certain rotating machine applications such as pumps or turbines since a flow passage must be provided through the center of the bearing.
Referring now to prior art FIG. 15, a hydrodynamic bearing is illustrated. In this embodiment, a bearing 126 has a tapered channel 128 filled with fluid represented by arrows 130. A runner 132 rotates in a direction represented by arrow 134. Axial force is represented by arrow 136. As runner 132 rotates in the direction of arrow 134, fluid is drawn out of tapered channel 128 into the gap 138 between runner 132 and bearing 126. Essentially, the fluid represented by arrows 130 is dragged from tapered channel 128 by the surface of runner 132. The pressure in the tapered channel increases with the speed of the runner, with decreasing clearance between runner 132 and bearing 126, and by increasing the viscosity of the fluid.
Referring now to prior art FIG. 16, bearing surface 142 contains tapered channels 144 such as that shown in prior art FIG. 15. As runner 146 rotates near bearing surface 142, fluid is provided by port 148 to cavity 150 and into tapered channel 144. Tapered channels 144 are in fluid communication with the cavity 150 to provide a source of fluid into tapered channels 144 to maintain a supply of fluid on bearing surface 142. In this configuration, the deep portion is represented by 152, and the shallow portion of tapered channel 144 is represented by 154. The direction of rotation of runner 146 in this configuration is in the counterclockwise direction.
In certain situations each of the configurations shown do not provide sufficient lubrication between the runners and the bearings. The inadequate lubrication reduce the life of the thrust bearing. Further, neither of the configurations shown provide for a flow passage through the center of the bearing. Many pumps require an axial flow passage through the center of the bearing.
It would therefore be desirable to provide an improved thrust bearing which provides increased lubrication between a rotating runner and a bearing and which further has the capability of being adapted to accommodate a flow passage through the center of the bearing.